Answer;
-Y- rays
Step-by-step explanation;
-The three types that were discovered were classified according to their penetrative ability and electrical charge: and named alpha, beta and gamma.
-Alpha are fast moving helium atoms. They have high energy due to their large mass, they are stopped by just a few inches of air, or a piece of paper.
-Beta are fast moving electrons. They typically have energies in the range of a few hundred keV to several MeV. Since electrons are might lighter than helium atoms, they are able to penetrate further, through several feet of air, or several millimeters of plastic or less of very light metals.
-Gamma are photons, just like light, except of much higher energy, typically from several keV to several MeV. Depending on their energy, they can be stopped by a thin piece of aluminum foil, or they can penetrate several inches of lead.